Francisco J. Gil-Bea

Cholinergic-serotonergic imbalance contributes to cognitive and behavioral symptoms in Alzheimer's disease

Neuropsychiatric symptoms seen in Alzheimers disease (AD) are not simply a consequence of neurodegeneration, but probably result from differential neurotransmitter alterations, which some patients are more at risk of than others. Therefore, the hypothesis of this study is that an imbalance between the cholinergic and serotonergic systems is related to cognitive symptoms and psychological syndromes of dementia (BPSD) in patients with AD. Cholinergic and serotonergic functions were assessed in post-mortem frontal and temporal cortex from 22 AD patients who had been prospectively assessed with the Mini-Mental State examination (MMSE) for cognitive impairment and with the Present Behavioral Examination (PBE) for BPSD including aggressive behavior, overactivity, depression and psychosis. Not only cholinergic deficits, but also the cholinacetyltransferase/serotonin ratio significantly correlated with final MMSE score both in frontal and temporal cortex. In addition, decreases in cholinergic function correlated with the aggressive behavior factor, supporting a dual role for the cholinergic system in cognitive and non-cognitive disturbances associated to AD. The serotonergic system showed a significant correlation with overactivity and psychosis. The ratio of serotonin to acetylcholinesterase levels was also correlated with the psychotic factor at least in women. It is concluded that an imbalance between cholinergic-serotonergic systems may be responsible for the cognitive impairment associated to AD. Moreover, the major findings of this study are the relationships between neurochemical markers of both cholinergic and serotonergic systems and non-cognitive behavioral disturbances in patients with dementia.

Lack of localization of 5‐HT6 receptors on cholinergic neurons: implication of multiple neurotransmitter systems in 5‐HT6 receptor‐mediated acetylcholine release

The involvement of the cholinergic system in learning and memory together with the cognitive enhancing properties of 5‐HT6 receptor antagonists led us to study the relationship between 5‐HT6 receptors and cholinergic neurotransmission. A selective cholinergic lesion, induced by injection of the immunotoxin 192‐IgG‐Saporin into the nucleus basalis magnocellularis, failed to alter the density of 5‐HT6 receptor mRNA or protein expression in the deafferentated frontal cortex, suggesting that 5‐HT6 receptors are not located on cholinergic neurons. The 5‐HT6 receptor antagonist SB‐357134 (0.001–1 µm) induced a concentration‐dependant K+‐evoked [3H]acetylcholine (ACh) release in vitro in rat cortical and striatal slices, which was blocked by tetrodotoxin. SB‐357134, up to 1 µm, stimulated glutamate release in cortical and striatal slices. In the cortex, riluzole (1 µm) blocked the SB‐357134‐induced K+‐stimulated [3H]ACh release, and simultaneous administration of MK‐801 (1 µm) and SB‐357134 (0.05 µm) elicited an increase in K+‐evoked ACh release. In the striatum, SB‐357134, 1 µm, decreased dopamine release, and the increase in K+‐evoked [3H]ACh release induced by 5‐HT6 receptor blockade was reversed by the D1 receptor antagonist, SCH23390 (1 µm). In both the frontal cortex and striatum, bicuculline, 1 µm, showed no effect on SB‐357134‐evoked [3H]ACh. These results are discussed in terms of neurochemical mechanisms involved in 5‐HT6 receptor functions.

Increased sensitivity to MPTP in human alpha-synuclein A30P transgenic mice.

In addition to genetic factors, environmental factors have long been suspected to contribute to the pathogenesis of Parkinsons disease (PD). We investigated the possible interaction between genetic factors and neurotoxins by testing whether alpha-synuclein A30P Tg5093 transgenic mice show increased sensitivity to secondary toxic insults like 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or rotenone. While sensitivity to chronic treatment with rotenone was not enhanced in the Tg5093 line, chronic treatment with 80 or 150 mg/kg MPTP resulted in increased deterioration of the nigrostriatal dopaminergic system as assessed by quantitation of nigral tyrosine hydroxylase (TH) positive neurons and striatal dopamine (DA) levels in Tg5093 mice when compared to non-transgenic littermate controls. Thus, the results of this study demonstrate a role for the overexpression of mutant human alpha-synuclein A30P in increased vulnerability of DA neurons to MPTP.

Cardiotrophin-1 is a key regulator of glucose and lipid metabolism.

Cardiotrophin-1 (CT-1) is a member of the gp130 family of cytokines. We observed that ct-1(-/-) mice develop mature-onset obesity, insulin resistance, and hypercholesterolemia despite reduced calorie intake. Decreased energy expenditure preceded and accompanied the development of obesity. Acute treatment with rCT-1 decreased blood glucose in an insulin-independent manner and increased insulin-stimulated AKT phosphorylation in muscle. These changes were associated with stimulation of fatty acid oxidation, an effect that was absent in AMPKα2(-/-) mice. Chronic rCT-1 treatment reduced food intake, enhanced energy expenditure, and induced white adipose tissue remodeling characterized by upregulation of genes implicated in the control of lipolysis, fatty acid oxidation, and mitochondrial biogenesis and genes typifying brown fat phenotype. Moreover, rCT-1 reduced body weight and corrected insulin resistance in ob/ob and in high-fat-fed obese mice. We conclude that CT-1 is a master regulator of fat and glucose metabolism with potential applications for treatment of obesity and insulin resistance.

Effects of 5-HT6 receptor antagonism and cholinesterase inhibition in models of cognitive impairment in the rat.

The beneficial effect of 5‐HT6 receptor antagonism in cognition remains controversial. This study has been undertaken to reassess the cognition enhancing properties of acute vs subchronic treatment with the selective 5‐HT6 receptor antagonist SB‐271046 in unimpaired rats, as well as against scopolamine (cholinergic‐) or MK‐801 (glutamatergic‐mediated) deficits.

Neonatal stress affects vulnerability of cholinergic neurons and cognition in the rat: Involvement of the HPA axis

Adverse experiences early in life may sensitize specific neurocircuits to subsequent stressors. We have evaluated in maternal separation (MS) rats, an animal paradigm of early-life stress, the effects of a selective cholinergic lesion on cognitive function as well as susceptibility of cholinergic neurons to the lesion. MS rats subjected to a cholinergic lesion by administration of the immunotoxin 192 IgG-saporin, showed significant decreases in both choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity compared to control lesioned rats. Morris water maze results revealed a significant impairment in learning and memory function in MS adult rats and further cognitive deficits after the lesion. The lesion of cholinergic neurons induced a significant decrease in glucocorticoid receptor density in MS rats, accompanied by increases in CRF mRNA expression. Decreases in NGF and increases in NGF-p75NTR expression have also been found in MS rats. Our results suggest that vulnerability of basal forebrain cholinergic nerve cells might be affected by the HPA axis. The present data are discussed not only in terms of conditions that occur during ageing or Alzheimer disease, but also regarding a purported involvement of the cholinergic system in the regulation of HPA axis activity.

Increase of locomotor activity underlying the behavioral disinhibition in tg2576 mice.

The transgenic Tg2576 mouse is a widely used animal model that develops some of the cognitive and neuropathological deteriorations observed in patients suffering Alzheimers disease. The authors investigated 9-month-old Tg2576 mice with respect to behavioral and endocrinological (hypothalamic- pituitary-adrenal [HPA] axis activity) parameters. The locomotor activity test revealed that Tg2576 mice moved almost twice as much as controls. Tg2576 mice spent significantly more time visiting the open arms and performed more entries into these open arms than did controls. However, the amount of time that Tg2576 mice remained in each entry to the open arm was similar to that of controls, and the number of arm entries correlated positively to locomotor activity. In the forced swimming test, Tg2576 mice showed a significant decrease in immobility time, which correlated negatively to locomotor activity. Parameters of the HPA axis, such as plasma level of corticosterone, adrenal gland weight, and noradrenaline or adrenaline release, did not differ between controls and Tg2576 mice. These data suggest that the disinhibitory behavior of Tg2576 mice seems to be related to increased locomotor activity but not to any disturbance of the HPA axis.

Involvement of the GABAergic system in depressive symptoms of Alzheimer's disease

Cognitive and neuropsychiatric (BPSD) symptoms seen in Alzheimers disease (AD) probably result from differential neurotransmitter alterations. The involvement of the glutamatergic and GABAergic system in cognitive and behavioral and psychological symptoms of dementia (BPSD) has been studied in post-mortem frontal and temporal cortex from AD patients who had been prospectively assessed with the Mini-Mental State Examination (MMSE) for cognitive impairment and with the Present Behavioral Examination (PBE) for BPSD. In addition to cholinergic deficits, significant decreases in gamma-amino butyric acid (GABA) content, with no changes in glutamate content, were found in frontal and temporal cortex. Both GABA levels and the glutamate/GABA ratio showed significant correlations with depression in AD. In the temporal cortex, higher densities of GABA(A)/benzodiazepine receptors also correlated with more severe depression. It can be suggested that in a situation of cholinergic deficit, such as AD, an imbalance between the excitatory glutamatergic tone and inhibitory GABAergic tone may be responsible for non-cognitive behavioral disturbances.

ALS: A bucket of genes, environment, metabolism and unknown ingredients

The scientific scenario of amyotrophic lateral sclerosis (ALS) has dramatically changed since TDP-43 aggregates were discovered in 2006 as the main component of the neuronal inclusions seen in the disease, and more recently, when the implication of C9ORF72 expansion in familial and sporadic cases of ALS and frontotemporal dementia was confirmed. These discoveries have enlarged an extense list of genes implicated in different cellular processes such as RNA processing or autophagia among others and have broaden the putative molecular targets of the disease. Some of ALS-related genes such as TARDBP or SOD1 among others have important roles in the regulation of glucose and fatty acids metabolism, so that an impairment of fatty acids (FA) consumption and ketogenic deficits during exercise in ALS patients would connect the physiopathology with some of the more intriguing epidemiological traits of the disease. The current understanding of ALS as part of a continuum with other neurodegenerative diseases and a crossroads between genetic, neurometabolic and environmental factors represent a fascinating model of interaction that could be translated to other neurodegenerative diseases. In this review we summarize the most relevant data obtained in the ten last years and the key lines for future research in ALS.

Analysis of chiral amino acids in cerebrospinal fluid samples linked to different stages of Alzheimer disease

Chiral micellar electrokinetic chromatography with laser‐induced fluorescence detection (chiral‐MEKC‐LIF) was used to investigate D‐ and L‐amino acid contents in cerebrospinal fluid (CSF) samples related to different Alzheimer disease (AD) stages. CSF samples were taken from (i) control subjects (S1 pool), (ii) subjects showing a mild cognitive impairment who remained stable (S2 pool), (iii) subjects showing an mild cognitive impairment that progressed to AD (S3 pool) and (iv) subjects diagnosed with AD (S4 pool). The optimized procedure only needed 10 μL of CSF and it included sample cleaning, derivatization with FITC and chiral‐MEKC‐LIF separation. Eighteen standard amino acids were baseline separated with efficiencies up to 703 000 plates/m, high sensitivity (LODs in the nM range) and good resolution (values ranging from 2.6 to 9.5). Using this method, L‐Arg, L‐Leu, L‐Gln, γ‐aminobutyric acid, L‐Ser, D‐Ser, L‐Ala, Gly, L‐Lys, L‐Glu and L‐Asp were detected in all the CSF samples. S3 and S4 samples (i.e. AD subjects) showed significant lower amounts of L‐Arg L‐Lys, L‐Glu and L‐Asp compared to the non‐AD S1 and S2 samples, showing in the S4 group the lowest amounts of L‐Arg L‐Lys, L‐Glu and L‐Asp. Moreover, γ‐aminobutyric acid was significantly higher in AD subjects with the highest amount also found for S4. No significant differences were observed for the rest of amino acids including D‐Ser. Based on the obtained chiral‐MEKC‐LIF data, it was possible to correctly classify all the samples into the four groups. These results demonstrate that the use of enantioselective procedures as the one developed in this work can provide some new light on the investigations of AD, including the discovery of new biomarkers related to different stages of AD.